The term 'sleep lightly' can be defined by the following crossword solutions: SNOOZE (6 letters), DROWSE (6 letters), DOZE (4 letters), NAP (3 letters), and CATNAP (6 letters). SNOOZE is a light sleep, usually taken during the day, while DROWSE is a state between sleeping and waking. DOZE is a light sleep, usually of short duration, and NAP is a short period of sleep during the day. Finally, CATNAP is a very short sleep, usually taken during the day.